Back-stand grinder



May 12, 1953 R. w. REED 2,637,952

BACK-STAND GRINDER l Filed Nov. 14, 1949 Patented May 12, 1953 UNITED STATES PATENT GFFICE BACK-STAN D GRINDER Application November 14, 1949, Serial No. 127,065

2 Claims. l

This invention relates to grinding or polishing machines, of the back-stand type, employing a coated abrasive belt. In machines of this type, a cloth belt, coated on its external surface with abrasive particles, travels over a resilient contact Wheel, and the sheet or other object to be abraded or polished is applied against the abrasivecoated surface of the belt along the portion of the belt that i-s backed by the contact wheel.

In machines of this type, it is quite dilcult to maintain the abrasive belt under uniform tension, due to the tendency of the belt to stretch after it has been subjected for a short time to the severe abrading operations which are normal in machine grinding and due to surface variations in the workpiece presented to the abrasive belt. Changes inthe belt tension are obviously undesirable in that the belt may slip from the contact wheel and such changes in tensio-n often result in uneven abrading of the workpiece.

A particular object of the invention, therefore, is the provision of an improved device for maintaining an abrasive belt under uniform tension under variable working conditions throughout the belt life. A further object is to provide a back-stand grinder which is simple and economi cal to construct and requires a minimum amount of machining, casting and stamping and eliminates links and levelers that are required in the conventional machines.

The foregoing advantages have been attained by me in a back-standv grinder employing a torsion-type spring. My machine is capable of preloading for extreme demands of tension; that is, a low tension may be provided for narrow belts of 1K2 inch width or less and a higher tension may be provided for belts of 3 inches or more in width. I have found that a back-stand grinder, in which the tension takeup is provided by a torsion type spring including a clock type spring, eliminates the links and levelers that are necessary with a compression type spring loaded back stand. Additionally my device is capable of greater tension takeup in belt stretch for the size of the unit than is the compression spring type. The machine also includes an improved tracking arrangement having a wide lateral adju-stmentthat retains the pulley parallel to the contact wheel at all times. This feature is especially important when extremely soft contact wheels or narrow contact wheels are employed in the grindingr machine.

The invention will be readily understood from the following description in conjunction with the accompanying drawing in which:

Figure l is a side elevational view of a backstand grinding machine embodying my invention;

Figure 2, a rear elevational view of the machine; and

Figure 3, a graph comparing load loss in pounds in the grinding device of Figs. l and 2 with a conventional compression spring loaded device, for the same amounts of belt stretch.

Referring to the drawing, the reference character 3 indicates a iront stand of conventional construction. A resilient contact wheel 4, supporting an abrasive belt 5, is mounted on a shaft G suitably journalled on the top of the front stand t. The shaft 5 carries a driving pulley I and belt 8 that is driven by a motor S. The contact wheel :t may be of any suitable resilient construction and may comprise a resilient wheel of the type` disclosed in U. S. Patents Nos. 2,145,418; 2,162,279; and 2,477,602. Such wheels are adapted toeprovide a resilient support for the abrasivebelt 5 aseit engages the workpiece to be abraded or polished, which may have an uneven surface. l

The back stand includes a U-'shaped base member lil, a channel-shaped rocker arm II pivotally mounted on the base member IG, and .an arbor I2 threaded through the upper portion of the rocker arm. II. An idler pulley I3, about which the abrasive belt 5 passes, is journalled on one end of arbor I2 and a track adjustment wheel I 4 `is iXedly mounted on the other end of the arbor. The central portion I5 of the arbor I2 is threaded to provide a wide lateral adjustment for the` idler I3 to keep it parallel to the contact wheel 'Il at all times. A locking pin I6 extends through the top of arm II and normally bears against arbor I2 to secure it against rotation in its apertures in the upper part of arm II.

The rocker arm l! is mounted on a gudgeon 'il vextending through the base member l0. A torsion spring I8 is also carried on the gudgeon. One end' I9 of the torsion spring bears against a stop member 2l) carried on one side of the rocker arm Il. The other end 2l of the torsion springs bears against a tension adjustment bolt 22 movably mounted in a vertical direction in a slotted bracket 23 carried on an extension 24 of base member in.

It is thus apparent that the spring I3 yieldably urges the rocker arm II and the idler I3 in a counterclockwise direction (Fig. l), away from the contact wheel li. The abrasive belt 5 may be readily placed about the contact wheel 4 and the idler pulley I3, and also removed therefrom, by rotating the rocker arm II in a clockwise direction from the position shown in Fig. 1. The spring I8 is capable of being preloaded for extreme demands of tension over a range of approximately 20 pounds to a maximum of over 100 pounds. Low tension is applied for narrow belts of l/2 inch or less in width and higher tension for belts up to 3 inches or more in width. Lowering the position of the spring extension 2l increases the tension on the abrasive belt.

All conventional cloth-backed abrasive belts stretch somewhat when subjected to usage in a grinding machine. The amount of stretch will vary in different belts depending upon the length and width of the belt, the type of backing, the

severity of the abrading operation and the amount of preioaded tension. A belt stretch of 4 to 6 inches is not uncommon in a belt 138 inches in length. A particular feature of my improved back-stand grinder is its capacity for maintaining the belt tension well above the critical range even though the belt may stretch up to 12 inches during the abrading operation.

This property is illustrated in the graph of Fig. 3 in which the load on the same type of abrasive belt was measured on my improved grinding machine for various amounts of belt stretch and on a conventional back-stand grinder of appproximately the same size and employing a compression spring device. In the graph the ordinate indicates load on the belt in pounds and the abscissa indicates belt stretch divided by two or idler pulley movement in inches. The load loss as the belt stretched on the compression spring grinder is shown in the unbroken line. improved grinder when given a minimum preloading is shown in the dashed line and the load loss on my improved grinder when preloaded for a maximum tension is shown in a dotted line. The same type of belt and of the same dimensions was used in all the tests.

It is apparent from the drawing that when the abrasive belt stretched 4 inches, resulting in the movement of the idler pulley to the extent of 2 inches, that the belt load on the standard compression spring grinder dropped from an original load of over 60 pounds to zero. In my backstand grinder using the same type of belt, and a preloading of minimum tension, the load on the belt dropped from 60 pounds to a little above 40 I.

pounds when the belt was stretched 4 inches. In the same device when the belt was preloaded to a maximum tension the load dropped from 110 pounds to a little above 70 pounds when the belt became stretched in the amount of 4 inches. It is also apparent from the graph that belts may be stretched 12 inches or more upon my backstand grinder, preloaded to a minimum or maximum tension, and still retain a substantial load on the belt under the stretched condition. Thus I am able in my improved back-stand grinder` to not only retain the belt upon a contact wheel and The load loss as the belt stretched on my 4 idler pulley under conditions of extremely abnormal belt stretch, but I am also able to obtain an even abrading action which is not possible with a loosely-mounted belt.

What I claim is:

1. In a grinding and polishing machine including a front stand having a motor-driven wheel and a coated abrasive belt trained thereon, a back-stand comprising a base member having spaced vertical supports, a yoke with its arms pivotally mounted on the supports of said base member, an arbor threaded in the upper portion of said yoke, an idler wheel, adapted to support one end of a coated abrasive belt, journalled on one end of saidv arbor, a track-adjustment member iixedly mounted upon the other end of said arbor, and manually rotatable to change the lateral position of said idler wheel, a locking member movably carried on the upper portion of the yoke and adapted to bear against the arbor to retain it imposition, a torsion spring vdevice mounted on the supports of said base member and between the arms of said yoke and secured thereto and yieldably urging said idler Wheel away from said driven-wheel, and means'for manually adjusting the tension on said torsion spring.

2. In a grinding and polishing machine includingr a front stand having a motor-driven wheel adapted to have a coated abrasive belt trained thereon, a back-stand comprising a base member having spaced vertical supports, a yoke with its arms pivotally mounted on the supports of said base member, and an arbor threaded in the upper portion of said yoke, an idler Wheel, adapted to support a coated abrasive belt, journalled on one end of said arbor, a torsion spring device mounted on the supports of said base member and between the arms of said yoke and secured thereto and adapted to yieldably urge said idler Wheel away from said driven-wheel, and means for manually adjusting the tension on said torsion spring.

RALPH W. REED.

References Cited in the le of this patent UNITED STATES PATENTS 

